Liquid carboxy-containing polyester oligomer, water-compatible polyurethane resin, and process for producing the same

ABSTRACT

A carboxy-containing polyester polyol which is obtained by polymerizing ε-caprolactone by ring-opening polymerization with a compound represented by the formula (1): HOCH 2 C(COOH)RCH 2 OH (1) (wherein R is C 2  or higher alkyl) and which has a number-average molecular weight of 550 to 950 and is liquid at ordinary temperature. This polyol can give a water-compatible polyurethane resin which is excellent in the preservation of a working atmosphere during handling and application and has excellent drying properties after application, and which has homogeneity and excellent stability and is useful in a wide range of applications such as a binder for coating materials, printing inks, etc. and an adhesive. By the production process, a water-compatible polyurethane resin which is excellent in the preservation of a working atmosphere and drying property and is homogeneous and stable can be easily produced.

FIELD OF THE INVENTION

The present invention relates to a water-dispersible polyurethane resinand a process for producing the same. More particularly, the presentinvention relates to a water-dispersible polyurethane resin and aprocess for producing the same, useful for applications such as coatingmaterials, binders, adhesives and the like.

BACKGROUND OF THE INVENTION

Water-dispersible polyurethane resins have been conventionally used ascoating materials, binders, adhesives and the like, due to excellentproperties thereof, such as flexibility, mechanical properties, adhesionproperties and the like. Recently, with a momentum for environmentalimprovement of trying to restrain organic solvent released to theatmosphere, the resins have been increasingly developed and utilized.

Heretofore, there have been many attempts to converting polyurethaneresins to water-dispersible ones through introducing hydrophilic groupsthereinto. Among these, anionic resins having carboxylate groupsintroduced into polyurethane chains are actively examined, due to goodwater-resistance. As methods for producing such resins, are mainly usedmethods comprising reacting a polyisocyanate compound with a polyol anda carboxyl group-containing diol such as dimethylol propionic acid togive an NCO-group terminated urethane prepolymer, neutralizing acarboxyl group thereof with a basic substance to disperse the prepolymerinto water, followed by chain-extending the prepolymer with a polyaminecompound (c.f. Patent documents 1 to 3).

In these methods, however, there has been problems, in obtainingurethane prepolymers, that dimethylol propionic acid has low solubilityin polyisocyanate compounds, polyols and usual low-boiling organicsolvents such as acetone and methylethylketone, and that, in case ofconducting reaction without any solvent or within a low-boiling organicsolvent, the reaction tends to become heterogeneous and result in gelledproducts. Besides, in order to conduct reaction to obtain prepolymer inhomogeneous system, it is compelled to use, as a solvent capable ofsufficiently dissolving dimethylol propionic acid, high-boilingsolvents, such as dimethyl formamide and N-methylpyrrolidone; and, sinceit is difficult to removed these high-boiling solvents after making theresin water-dispersible, there have been problems that high-boilingsolvents remained within final aqueous resin liquors deteriorates dryingproperty and working environment upon application of the resultingaqueous polyurethane resins.

On the other, it has reported in some publications (c.f. Patentdocuments 4 and 5) that a homogeneous and stable aqueous polyurethaneresins can be obtained, without deteriorating drying property andworking environment upon application, through reacting a polyisocyanatecompound with a carboxyl group-containing polyester polyol obtainable byring-opening polymerization of ε-caprolactone to a dimethylol alkanoicacid, and the aqueous polyurethane resins can be manufactured easily. Inthese specifications, however, merely an addition of caprolactone todimethylol propionic acid was described in Example, and there were nodescription of an adduct of caprolactone to a dimethylol alkanoic acidrepresented by the formula (1) HOCH₂C(COOH)RCH₂OH (wherein R is an alkylgroup of not less than C₂) according to the present invention. Besides,there was no description that carboxyl group-containing polyester polyolwhich is liquid at ordinary temperature and has an average molecularweight within a specific range can be produced by examining in detailthe addition of caprolactone to a dimethylol alkanoic acid representedby the formula (1). (JP B 61-5485, JP B 03-48955, JP B 04-488, JP A06-313024, and JP A 08-27243)

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a water-dispersiblepolyurethane resin capable of providing a homogeneous and stabledispersion, and to provide a process for producing easily saidwater-dispersible polyurethane resin, through providing a carboxylgroup-containing polyester polyol liquid at ordinary temperature,without deteriorating working environment upon heating andpowder-charging operations and the like in manufacturing, and withoutdeteriorating drying property and working environment upon application

The inventors have reached the present invention, as a result ofextensive investigations, finding that a water-dispersible polyurethaneresin capable of providing a homogeneous and stable dispersion can beobtained by reacting a polyisocyanate compound with a polyol comprisinga carboxyl group-containing polyester polyol, liquid at ordinarytemperature, having a number-average molecular weight of 550 to 950 andbeing obtainable by ring-opening polymerization of ε-caprolactone to acompound represented by the formulaHOCH₂C(COOH)RCH₂0H  (1):(wherein R is an alkyl group containing at least 2 carbon atoms)followed by neutralizing a carboxyl group in a molecular chain with abasic substance.

DFTAILED DESCRIPTION OF THE INVENTION

The present invention is described in detail hereinafter.

The carboxyl group-containing polyester polyol, liquid at ordinarytemperature, according to this invention, is a polyester polyol having anumber-average molecular weight of 550 to 950 obtainable by ring-openingpolymerization of ε-caprolactone onto a compound represented by theformula (1) HOCH₂C(COOH)RCH₂OH (wherein, R is an alkyl group of not lessthan C₂). Dimethylol alkanoic acids, used in the invention, which arecompounds represented by the formula (1), include, for example,dimethylol butanoic acids, R in the formula (1) being ethyl group,dimethylol pentanoic acids, R in the formula (1) being propyl group, andthe like. Preferred are dimethylol butanoic acids, particularly2,2-dimethylol butanoic acid.

Catalysts used in the ring-opening polymerization of ε-caprolactone to adimethylol alkanoic acid, that is a carboxyl group-containing diolrepresented by the formula (1), include, for instance, organo-titaniumcompounds, such as tetraethyl titanate, tetrabutyl titanate andtetrapropyl titanate; organotin compounds, such as stannous octoate,dibutyltin oxide, dibutyltin dilaurate, mono-n-butyltin salts of fattyacid; and stannous halides such as stannous chloride, stannous bromideand stannous iodide, and the like.

It is preferred to use the above catalyst in an amount of 0 to 100 ppm,particularly 0 to 50 ppm, based on raw materials charged. In case ofcaprolactone addition to dimethylol butanoic acid, a ring-openingreaction of lactones can proceed even in the absence of the catalyst;while use of the catalyst in an amount of exceeding 100 ppm is notpreferred, causing a too rapid ring-opening reaction and resulting inpoor properties, such as durability and water-resistance, of syntheticresins prepared using the resultant compounds.

Ring-opening polymerization of ε-caprolactone to a dimethylol alkanoicacid, that is a carboxyl group-containing diol represented by theformula (1), is preferably carried out at a reaction temperature in therange from 60 to 180° C., more preferably from 70 to 150° C. If thereaction temperature is less than 60° C., the ring-opening reaction oflactone is too slow to be economically accepted. On contrast, if above180° C., undesirable gelation is occurred by an intermoleculardehydration reaction. Additionally, it is possible to attain betterresults in color of products and so on, through conducting synthesisduring the reaction within an inert atmosphere such as nitrogen gas.

The above carboxyl group-containing polyester polyol, liquid at ordinarytemperature, represented by the formula (1), has a number-averagemolecular weight of necessarily 550 to 950, preferably 550 to 800, andmore preferably 600 to 700. Ones having a number-average molecularweight less than 550 and ones of above 950 are solid at ordinarytemperature; and are not preferred with respect to conductingoperations, since additional steps such as pre-heating to melt saidcompound are required upon using such as in charging operation into areactor.

Content of carboxyl group in the water-dispersible polyurethane resinaccording to this invention, which can be controlled depending uponindicated uses, is preferably 0.4 to 5% by weight based on the solid ofwater-dispersible polyurethane resin. When the content of carboxyl groupis below 0.4% by weight, it is difficult to make the resinwater-dispersible; while such a content of carboxyl group exceeding 5%by weight results in resins of poor coating properties.

Together with the carboxyl group-containing polyester polyol having anumber-average molecular weight of 550 to 950 obtainable by ring-openingpolymerization of ε-caprolactone to a dimethylol alkanoic acid or acarboxyl group-containing diol represented by the formula (1) as aninitiator, there may be used as a polyol component in the presentinvention a polyol or polyols other than the carboxyl group-containingpolyester polyol. Content of carboxyl group in the solid of aqueouspolyurethane resin according to the present invention can be controlledby, for example, changing the proportion of the carboxylgroup-containing polyester polyol within the polyol component.

Examples of polyols other than the carboxyl group-containing polyesterpolyol optionally used in the present invention include ones having anaverage molecular weight around 400 to 5000, for example, polyetherpolyols, such as polytetramethylene ether glycol, polypropylene glycoland polyethylene glycol; polyester polyols, including bifunctionalpolyols having terminal hydroxyl groups obtainable by condensationreaction of a diol and a dicarboxylic acid such as polyethylene adipate,polyethylenebutylene adipate, polybutylene adipate, polypropyleneadipate, polyhexamethylene adipate, polyneopentylene adipate andpoly-3-methyl-1,5-pentylene adipate, condensation products of1,6-hexanediol, 3-methyl-1,5-pentanediol or the like with terephthalicacid alone or a combination thereof with isophthalic acid or adipicacid, and polycaprolactone, polymethylvalerolactone, and the like;polycarbonate polyols; silicone polyols; polybutadiene polyols;polyolefinic polyols and the like. These polyols may tae used alone orin combination of two or more of them.

Moreover, together with the above polyol component, there may beoptionally used short-chain dial or diols, such as ethylene glycol,propylene glycol, diethylene glycol, 1,4-butanediol, neopentyleneglycol, 1,6-hexanediol and 3-methyl-1,5-pentanediol. Polyisocyanatecompounds in the present invention include, for example, aromaticdiisocyanates, such as 4,4′-diphenylmethane diisocyanate, 2,4- or2,6-tolylene diisocyanate, 1,5-naphthalene diisocyanate and p- orm-phenylene diisocyanate; alicyclic diisocyanates, such as isophoronediisocyanate, 4,4′-dicyclohexylmethane diisocyanate, 1,4-cyclohexylenediisocyanate and hydrogenated tolylene diisocyanate; aliphaticdiisocyanates, such as hexamethylene diisocyanate; and xylylenediisocyanate, m-tetramethylxylylene diisocyanate and the like. Amongthese, preferred are alicyclic diisocyanates, because of being easy toprepared, stability of the resulting resin in water, and anti-yellowingproperties. These polyisocyanate compounds may be used alone or incombination of two or more of them.

The present invention is based on the finding that a water-dispersiblepolyurethane resin capable of providing a homogeneous and stabledispersion can be obtained, in introducing a carboxyl group into apolyurethane chain or a urethane prepozytner chain, through reaction ofa polyisocyanate compound with a polyester polyol, which has anumber-average molecular weight in a specific range and is obtainable byring-opening polymerization of ε-caprolactone preferably with dimethylolbutanoic acid. The carboxyl group in the polyurethane chain or urethaneprepolymer chain is preferably neutralized with a basic substance.

Basic substances, used for neutralizing the carboxyl group in thepolyurethane chain or urethane prepolymer chain in the presentinvention, include, for example, tertiary amines, such astrimethylamine, triethylamine, methyldiethylamine and tripropylamine;alkanol amines, such as dimethylethanolamine, methyldiethanolamine andtriethanolamine; ammonia; and hydroxides and carbonates of alkali metalssuch as sodium and potassium. More preferred are, for example, tertiaryamines and alkanol amines. The basic substance is preferably added in aratio of 0.5 to 1 equivalent to 1 equivalent of carboxyl group inurethane prepolymer.

Water-dispersible polyurethane resins in the present invention may beprepared by any known methods, not limited to specific ones. Preferredmethod is a method which comprises reacting a polyisocyanate compoundwith a polyol component comprising a carboxyl group-containing polyesterpolyol having a number-average molecular weight of 550 to 950 obtainableby ring-opening polymerization of ε-caprolactone to dimethylol butanoicacid as an initiator; neutralizing carboxyl groups in the resultingwater-soluble polyurethane resin with a basic substance to disperse ordissolve the resin into water; and chain-extending the resin with achain-extender to produce a water-dispersible polyurethane resin.

Water-dispersible polyurethane resins in this invention may be preparedby any known methods, not limited to specific ones. Preferred method isa method which comprises reacting a polyisocyanate compound with apolyol component containing carboxyl group-containing polyester polyolhaving a number-average molecular weight of 550 to 950 obtainable byring-opening polymerization of ε-caprolactone to dimethylol butanoicacid as an initiator, to prepare a urethane prepolymer having terminalNCO groups; neutralizing carboxyl group to disperse or dissolve theprepolymer into water; and chain-extending the prepolymer with achain-extender to prepare a water-dispersible polyurethane resin.

Preferable chain-extenders, optionally used for chain-extention ofurethane prepolymers having terminal NCO groups in the presentinvention, are polyamine compounds, for example, diamines, such asethylenediamine, 1,2-propanediamine, tetramethylenediamine,hexamethylene diamine, 1,4-cyclohexylenediamine, isophorondiamine,4,4′-dicyclohexylmethanediamine, m-xylylenediamine, phenylenediamine;polyethylene polyamines, such as diethylenetriamine,triethylenetetramine and tetraethylenepentamine; hydrazine; piperazine;and dihydrazide compounds of hydrazine with adipic acid or phthalic acidand the like. There may also be used short-chain diol or diols asmentioned above, These may be used alone or in combination of two ormore of of them. In combination with the polyamine compound, there maybe used monoethanolamine or diethanolamine to introduce hydroxyl groupsat the ends of the polyurethane, or there may be usedaminoethylaminoethanol to introduce hydroxyl groups on the main chain.

In the present invention, urethane prepolymer having terminal NCO groupsmay be reacted without any solvent and used as such. Alternatively,prepolymer may be diluted with a small amount of a low-boiling organicsolvent or may be prepared through reaction within a solution beforehandcontaining a small amount of low-boiling organic solvent, to reduceviscosity thereof, in order to facilitate afterward emulsification ofthe prepolymer with water into oil-in-water emulsions. In this case, itis generally preferred to react the polyisocyanate compound with thepolyol component in an equivalent ratio of NCO/OH=1.1/1 to 6/1.

Low-boiling organic solvents, used in the above reaction of urethaneprepolymers, are preferably removed after aquefication of the resin, andthus preferably have a boiling point of not more than 100° C. due to theease of removal, including, for instance, acetone, methylethylketone,tetrahydrofuran and the like. More preferred are acetone andmethylethylketone, particularly acetone.

It is preferred to conduct reaction of urethane prepolymer undernitrogen stream without any catalyst. When using a catalyst, there maybe used, for example, organometallic catalysts, such as dibutyltindilaurate, dibutyltin dioctoate and dibutyltin diacetate; and tertiaryamine catalysts, such as triethylenediamine. Reaction temperature ispreferably within the range from 20 to 120° C. Reaction time, which canbe varied depending upon the reaction temperature and so on of eachstage of reaction and not defined categorically, is preferably around 1to 20 hours.

In case of using an organic solvent in the reaction of thewater-dispersible polyurethane resin according to the present invention,there can be taken any methods to remove it, for example, a method ofremoving a solvent by feeding air, nitrogen gas or the like on or intoan obtained reaction solution, at a temperature not more than theboiling point of water, or at 30 to 100° C.; a method of removing asolvent under reduced pressure from the reaction vessel; and a method ofusing a thin film evaporator. Although another object of the presentinvention is to provide a water-dispersible polyurethane of almostorganic solvent-free, if an application allows use of a small amount oforganic solvent, an organic solvent may be used in the preparation ofthe water-dispersible polyurethane resin and allowed to remain in thereaction product as it is.

Water-dispersible polyurethane resins finally obtained according to thepresent invention usually have a solid content of 10 to 70% by weight,and polyurethane particles dispersed in water preferably have an averageparticle size of not more than 5 μm. Appearance of water-dispersiblepolyurethane resin of the present invention can be varied depending uponsize of dispersed particles. When an average particle size is smaller,the resin is in a fluorescent liquid state, and when an average particlesize is larger, the resin is white emulsion. In any case, it maintainsits nature in stable state over time. A solids content and a viscositycan be adjusted according to an application by controlling a particlesize of dispersed polyurethane. A polyurethane resin having lesshydrophilic groups therein tends to provide larger particle size whendispersed and those having more hydrophilic groups tend to providesmaller particle size. Water-dispersible polyurethane resins of thisinvention have a number-average molecular weight of preferably 6,000 to500,000, more preferably 7,000 to 300,000, and further more preferably8,000 to 150,000.

“A number-average molecular weight” as used herein refers a valueobtained by measuring with GPC at 1% by weight in tetrahydrofuran andconverting in the basis of polystyrene conversion calculation.Water-dispersible polyurethane resins of the invention are suitable forvarious applications, such as coating materials, binders, adhesives andthe like, and may be used as such in the form of one-component, or maybe used in the form of two-component, optionally mixed with awater-dispersible blocked isocyanate curative, an unblocked NCOgroup-containing water-dispersible isocyanate curative, a melaminiccurative, or a polyaziridine compound or the like as a cross-linker. Inthis case, the water-dispersible polyurethane resin may be optionallyblended with various additives, such as antioxidants, UV stabilizers,colorants, antifoaming agents, flow control agents, water repellants andfillers.

The present invention is further described in detail by the followingExamples below, but the present invention should not be restricted tothese the Examples without departing from the scope of the invention. InExamples, parts and % mean parts by weight and % by weight,respectively.

EXAMPLES Example 1

In a reaction vessel, 148 parts of dimethylol butanoic acid, 452 partsof ε-caprolactone and stannous octoate as a catalyst in a catalystconcentration of 5 ppm were charged, and heated under stirring within anitrogen stream to dissolve them uniformly, followed by reacting themfor 4 hours at 90° C. to give a carboxyl group-containing polyesterpolyol having a number-average molecular weight of 600. It is designatedas Polyol A.

Example 2

In a reaction vessel, 148 parts of dimethylol butanoic acid, 552 partsof ε-caprolactone and stannous octoate as a catalyst in a catalystconcentration of 5 ppm were charged, and reacted similarly as in Example1 to give a carboxyl group-containing polyester polyol having anumber-average molecular weight of 700. It is designated as Polyol B.

Example 3

In a reaction vessel, 148 parts of dimethylol butanoic acid, 652 partsof ε-caprolactone and stannous octoate as a catalyst in a catalystconcentration of 5 ppm were charged, and reacted similarly as in Example1 to give a carboxyl group-containing polyester polyol having anumber-average molecular weight of 800. It is designated as Polyol C.

Example 4

In a reaction vessel, 148 parts of dimethylol butanoic acid, 752 partsof ε-caprolactone and stannous octoate as a catalyst in a catalystconcentration of 5 ppm were charged, and reacted similarly as in Example1 to give a carboxyl group-containing polyester polyol having anumber-average molecular weight of 900. It is designated as Polyol D.

Comparative Example 1

In a reaction vessel, 148 parts of dimethylol butanoic acid, 352 partsof ε-caprolactone and stannous octoate as a catalyst in a catalystconcentration of Sppm were charged, and reacted similarly as in Example1 to give a carboxyl group-containing polyester polyol having anumber-average molecular weight of 500. It is designated as Polyol E.

Comparative Example 2

In a reaction vessel, 148 parts of dimethylol butanoic acid, 852 partsof ε-caprolactone and stannous octoate as a catalyst in catalystconcentration of 5 ppm were charged, and reacted similarly as in Example1 to give a carboxyl group-containing polyester polyol having anumber-average molecular weight of 1000. It is designated as Polyol F.

Comparative Example 3

In a reaction vessel, 134 parts of dimethylol propionic acid, 366 partsof ε-caprolactone and stannous octoate as a catalyst in a catalystconcentration of 5 ppm were charged, and reacted similarly as in Example1 to give a carboxyl group-containing polyester polyol having anumber-average molecular weight of 500. It is designated as Polyol G.

Comparative Example 4

In a reaction vessel, 134 parts of dimethylol propionic acid, 466 partsof ε-caprolactone and stannous octoate as a catalyst in a catalystconcentration of 5 ppm were charged, and reacted similarly as in Example1 to give a carboxyl group-containing polyester polyol having anumber-average molecular weight of 600. It is designated as Polyol H.

Comparative Example 5

In a reaction vessel, 134 parts of dimethylol propionic acid, 566 partsof ε-caprolactone and stannous octoate as a catalyst in a catalystconcentration of 5 ppm were charged, and reacted similarly as in Example1 to give a carboxyl group-containing polyester polyol having anumber-average molecular weight of 700. It is designated as Polyol I.

Comparative Example 6

In a reaction vessel, 134 parts of dimethylol propionic acid, 666 partsof ε-caprolactone and stannous octoate as a catalyst in catalystconcentration of 5 ppm were charged, and reacted similarly as in Example1 to give a carboxyl group-containing polyester polyol having anumber-average molecular weight of 800. It is designated as Polyol J.

Comparative Example 7

In a reaction vessel, 134 parts of dimethylol propionic acid, 766 partsof ε-caprolactone and stannous octoate as a catalyst in a catalystconcentration of 5 ppm were charged, and reacted similarly as in Example1 to give a carboxyl group-containing polyester polyol having anumber-average molecular weight of 900. It is designated as Polyol K.

Comparative Example 8

In a reaction vessel, 134 parts of dimethylol propionic acid, 866 partsof ε-caprolactone and stannous octoate as a catalyst in a catalystconcentration of 5 ppm were charged, and reacted similarly as in Example1 to give a carboxyl group-containing polyester polyol having anumber-average molecular weight of 1000. It is designated as Polyol L.

Observation results at 25° C. of Polyols A to L obtained by Examples 1to 4 and Comparative Examples 1 to B are shown in Table 1. TABLE 1Example Comparative Example 1 2 3 4 1 2 3 4 S 6 7 8 Polyol A B C D E F GH I J K L State at 250° C. Liquid Liquid Liquid Liquid Solid Solid SolidSolid Solid Solid Solid Solid DMBA or DMPA DMBA DMBA DMBA DMBA DMBA DMBADMPA DMPA DMPA DMPA DMPA DMPA Molecular 600 700 800 900 500 1000 500 600700 800 900 1000 weightDMBA: dimethylol butanoic acidDMPA: dimethylol propionic acid

Example 5

In a reaction vessel, 83.5 parts of isophorone diisocyanate, 111.6 partsof polytetramethylene ether glycol having a number-average molecularweight of 1000 and 54.9 parts of Polyol A obtained in Example 1 werecharged, and reacted under stirring for 5 hours at 80° C. withinnitrogen stream to give a homogeneous clear urethane prepolymer havingterminal NCO groups. Then, the prepolymer was cooled down to atemperature of 50° C. and neutralized with 9.24 parts of triethylamine.To this, was added 383.4 parts of demineralized water gradually toresult an oil-in-water urethane prepolymer dispersion, followed byadding thereto 33.22 parts of isophorone diamine and 299.0 parts ofdemineralized water at 10° C. to conduct a chain-extension of theprepolymer to obtain a water-dispersible polyurethane resin. Upon thefollowing tests, the resin had a solid content of 30%, a viscosity of150 mPa·s/25° C. and an average particle size of 5 am. The resin wascoated onto a glass plate at gap of 250 am, and dried for 2 hours at 80°C. to give a homogeneous clear and soft film of about 70 cm inthickness. The resulting film showed good physical properties of tensilestrength of 48 MPa and elongation of 600%, upon tensile test, afterallowing to stand for 1 day at 23° C. and 60% RH, according to thefollowing test method under the same environment. The resin had anumber-average molecular weight of 31,000 on the basis of polystyreneconversion calculation, upon dissolving the resultant film intetrahydrofuran to 1% concentration and measuring molecular weight withGPC (gel-permeation chromatography).

Example 6

In a reaction vessel, 80.6 parts of isophorone diisocyanate, 107.6 partsof polytetramethylene ether glycol having a number-average molecularweight of 1000 and 61.8 parts of Polyol B obtained in Example 2 werecharged, and reacted under stirring for 5 hours at 80° C. withinnitrogen stream to give a homogeneous clear urethane prepolymer havingterminal NCO groups. Then, the prepolymer was cooled down to atemperature of 50° C. and neutralized with 8.91 parts of triethylamine.To this, was added 382.6 parts of demineralized water gradually toresult an oil-in-water urethane prepolymer dispersion, followed byadding thereto 33.22 parts of isophorone diamine and 299.0 parts ofdemineralized water at 10° C. to conduct a chain-extension of theprepolymer to obtain a water-dispersible polyurethane resin. Upon thefollowing tests, the resin had a solid content of 30%, a viscosity of140 mPa·s/25° C. and an average particle size of 5 μm. Then, ahomogeneous clear film was obtained similarly as in Example 5, and theresulting film showed good physical properties of tensile strength of 44MPa and elongation of 600%, upon tensile test according to the followingtest method. The resin had a number-average molecular weight of 43,000.

Comparative Example 9

In a reaction vessel, 86.7 parts of isophorone diisocyanate, 115.8 partsof polytetramethylene ether glycol having a number-average molecularweight of 1000 and 47. 5 parts of Polyol E obtained in ComparativeExample 1, liquefied by pre-heating within an oven for 1 day at 60° C.,were charged, and reacted under stirring for 5 hours at 80° C. withinnitrogen stream to give a homogeneous clear urethane prepolymer havingterminal NCO groups. Then, the prepolymer was cooled down to atemperature of 50° C. and neutralized with 9.59 parts of triethylamine.To this, was added 384.2 parts of demineralized water gradually toresult an oil-in-water urethane prepolymer dispersion, followed byadding thereto 33.22 parts of isophorone diamine and 299.0 parts ofdemineralized water at 10° C. to conduct a chain-extension of theprepolymer to obtain a water-dispersible polyurethane resin. Upon thefollowing tests, the resin had a solid content of 30%, a viscosity of180 mPa·s/25° C. and an average particle size of 5 μm. Then, ahomogeneous clear film was obtained similarly as in Example 5, and theresulting film showed good physical properties of tensile strength of 52MPa and elongation of 580%, upon tensile test according to the followingtest method. The resin had a number-average molecular weight of 43,000.The measurement methods of physical properties in Examples are asfollows.

Test Methods

(1) Viscosity

Viscosity (mPa·s) at 25° C. was measured with a rotary viscometer ofEM-type, manufactured by Tokyo Keiki Co. Ltd., with respect to aqueoussolutions of water-dispersible polyurethane resins, afterchain-extention, obtained in Examples 5 and 6 and Comparative Example 9.

(2) Average Particle Size

Average particle size (μm) was measured with a viscosity profilemeasurement apparatus manufactured by HORIBA Ltd., with respect toaqueous solutions of water-dispersible polyurethane resins, afterchain-extention, obtained in Examples 5 and 6 and Comparative Example 9.

particle size (μm) with a viscosity profile measurement apparatus,manufactured by HORIBA Ltd.,

(3) Physical Properties

With respect to films obtained in Examples 5 and 6 and ComparativeExample 9, each film was die-cut into 10×120 mm with a die cutter, andtensile strength (MPa) and elongation (%) were measured according to JISK 6301 at a tensile rate of 500 mm/min with a Tensilon UTM-III/-100model, manufactured by Toyo Baldwin Co. Ltd.

INDUSTRIAL APPLICABILITY

Water-dispersible polyurethane resins obtained according to the presentinvention provide excellent working environment and dryingcharacteristics during handling and application as well as excellenthomogeneity and stability, and are useful for a wide range ofapplications, for example, coatings, binders, such as ones for printinginks, adhesives and the like. Further, according to the productionprocess of the present invention, it is possible to produce easily awater-dispersible polyurethane resin providing excellent workingenvironment and drying characteristics as well as excellenk homogeneityand stability.

1. A carboxyl group-containing polyester polyol liquid at ordinarytemperature, having a number-average molecular weight of 550 to 950 andbeing obtainable by ring-opening polymerization of ε-caprolactone to acompound represented by the formula:HOCH₂C(COOH)RCH₂OH wherein R is an alkyl group containing at least 2carbon atoms.
 2. A carboxyl group-containing polyester polyol liquid atordinary temperature, according to claim 1, wherein the compoundrepresented by the formula is dimethylol butanoic acid.
 3. Awater-dispersible polyurethane resin, which is obtainable by reacting apolyisocyanate compound with a polyol component comprising the carboxylgroup-containing polyester polyol liquid at ordinary temperatureaccording to claim 1, and contains a carboxyl group neutralized with abasic substance within the molecular chain.
 4. A water-dispersiblepolyurethane resin according to claim 3, which contains the carboxylgroup in an amount of 0.4 to 5% by weight in the solid content of thewater-dispersible polyurethane resin.
 5. A water-dispersiblepolyurethane resin according to claim 3, wherein the water-dispersiblepolyurethane resin has a number-average molecular weight of 6,000 to500,000.
 6. A process for producing a water-dispersible polyurethaneresin, which comprises neutralizing, with a basic substance, carboxyl,group or groups of a water-dispersible polyurethane resin obtainable byreacting a polyisocyanate compound with the carboxyl group-containingpolyester polyol liquid at ordinary temperature according to claim 1, todisperse or dissolve the resin into water; and chain-extending thepolyurethane resin with a chain-extender.
 7. A process for producing awater-dispersible polyurethane resin, which comprises reacting apolyisocyanate compound with a polyol component comprising the carboxylgroup-containing polyester polyol, liquid at ordinary temperatureaccording to claim 1 to prepare a urethane prepolymer having terminalNCO groups; neutralizing, with a basic substance, carboxyl group orgroups of the prepolymer to disperse or dissolve the prepolymer intowater; and chain-extending the prepolymer with a chain-extender.
 8. Awater-dispersible polyurethane resin obtainable by the productionprocess according to claim
 6. 9. A water-dispersible polyurethane resin,which is obtainable by reacting a polyisocyanate compound with a polyolcomponent comprising the carboxyl group-containing polyester polyolliquid at ordinary temperature according to claim 2, and contains acarboxyl group neutralized with a basic substance within the molecularchain.
 10. A water-dispersible polyurethane resin according to claim 4,wherein the water-dispersible polyurethane resin has a number-averagemolecular weight of 6,000 to 500,000.
 11. A process for producing awater-dispersible polyurethane resin, which comprises neutralizing, witha basic substance, carboxyl, group or groups of a water-dispersiblepolyurethane resin obtainable by reacting a polyisocyanate compound withthe carboxyl group-containing polyester polyol liquid at ordinarytemperature according to claim 2, to disperse or dissolve the resin intowater; and chain-extending the polyurethane resin with a chain-extender.12. A process for producing a water-dispersible polyurethane resin,which comprises reacting a polyisocyanate compound with a polyolcomponent comprising the carboxyl group-containing polyester polyol,liquid at ordinary temperature according to claim 2 to prepare aurethane prepolymer having terminal NCO groups; neutralizing, with abasic substance, carboxyl group or groups of the prepolymer to disperseor dissolve the prepolymer into water; and chain-extending theprepolymer with a chain-extender.
 13. A water-dispersible polyurethaneresin obtainable by the production process according to claim 7.